Faculty Research at Morehead State University


Dirk Grupe

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We present an analysis of historical multi-wavelength emission of the Changing Look (CL) Active Galactic Nucleus (AGN) in NGC 2992, covering epochs ranging from 1978 to 2021, as well as new X-ray and optical spectra. The galaxy presents multiple Seyfert type transitions from type 2 to intermediate-type, losing and regaining its H𝛼 BEL recurrently. In X-rays, the source shows intrinsic variability with the absorption corrected luminosity varying by a factor of 40. We rule-out tidal disruption events or variable obscuration as causes of the type transitions, and show that the presence and the flux of the broad H𝛼 emission line are directly correlated with the 2-10 keV X-ray luminosity (L210): the component disappears at L210 261042 erg cm2 s1, this value translates into an Eddington ratio (𝜆Edd) of 1%. The 𝜆Edd in which the BEL transitions occur is the same as the critical value at which there should be a state transition between a radiatively inefficient accretion flow (RIAF) and a thin accretion disk, such similarity suggests that the AGN is operating at the threshold mass accretion rate between the two accretion modes. We find a correlation between the narrow Fe K𝛼 flux and 𝜆Edd, and an anti-correlation between full-width at half maximum of H𝛼 BEL and 𝜆Edd, in agreement with theoretical predictions. Two possible scenarios for type transitions are compatible with our results: either the dimming of the AGN continuum, which reduces the supply of ionising photons available to excite the gas in the Broad Line Region (BLR), or the fading of the BLR structure itself occurs as the low accretion rate is not able to sustain the required cloud flow rate in a disk-wind BLR model.



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